Acrylonitrile (ACRN) is an important monomer for the synthesis of various polymers including acrylic fibers, synthetic rubbers, nylons, and is the starting material for acrylic acids and acrylamide. Processes to prepare ACRN include the Sohio Process in which propylene reacts with ammonia and oxygen (air) over a catalyst at elevated temperatures (“ammoxidation”). Hydrogen cyanide (HCN) and acetonitrile (AN) are produced as by-products.
HCN is a valuable by-product and is used, for example, as a starting material for the synthesis of various polymers, including polyamides, and chemicals.
Methanol injection to the ACRN reactor can increase HCN production in the Sohio Process, decreasing the ACRN:HCN weight ratio in the raw effluent from 10:1 to 8:1.
U.S. Pat. No. 8,585,870 discloses a method for co-manufacturing HCN and ACRN from separate reactor systems with a combined recovery/purification system. The disclosed process charges the HCN reactor effluent to an absorber column and the ACRN reactor effluent to a quench column. The process then shares a combined recovery/purification system. Under some conditions, the combined recovery/purification process can form insoluble solids that can accumulate and plug equipment. The problem can be more noticeable at lower ACRN:HCN weight ratios (higher levels of HCN co-production).